The present invention relates generally to the production of conductive polymers and in particular, to the production of highly conductive polymers having selectively located n and p regions produced by ion irradiation to facilitate the fabrication of microelectronic circuitry on the polymers.
The growing interest in the industrial exploitation of outer space has created a demand for microelectronic components that are both light weight and tolerant of relatively high radiation levels. Certain military applications also require light weight, radiation-resistant microelectronic components. While semiconductor microelectronic components made from gallium arsenide are known which can withstand between 10.sup.8 to 10.sup.9 rads, these components are relatively heavy and hence expensive to transport to space While light weight microelectronic components formed from conductive polymers are also known, the resulting components are generally unstable when exposed to normal levels of oxygen and to significant levels of radiation.
The use of conductive polymers in the fabrication of microelectronic circuitry initially appeared promising. Circuit devices made from such polymers are not only light weight; the costs of the polymeric materials are significantly less than the cost of more conventional semiconductor materials. In addition, polymeric films are flexible and permit the fabrication of large sections of circuitry with relative ease. However, each of the currently available methods for making polymeric films conductive has its shortcomings.
One such available method for producing a conductive polymer involves chemically doping the polymer with a suitable oxidizing or reducing agent. This technique not only increases the conductivity of the polymer, but it also determines whether the type of conductivity will be p or n. Unfortunately, the resulting conductivity is not stable, and when a chemically doped conductive polymer produced according to this method is exposed to the oxygen and moisture present in air, the conductivity decreases with time. After a period of time, the polymer may no longer be capable of functioning as required in an electronic circuit. For example, polyacetylene, a polymer that is both highly conductive and easy to prepare, reacts so quickly with ambient oxygen that the deterioration of its conductive properties becomes evident after just ten minutes exposure to air.
In another method, highly conductive polymers are made by irradiating the polymers with ions. Although these polymers are both highly conductive and stable, their utility in electronic circuit applications is limited by the fact that the type of conductivity (p or n) that is ion-produced is specific to each polymer. Hence, the entire polymer has only a single type of conductivity after irradiation. Consequently, two polymer types, one of which has p conductivity and the other of which has n conductivity after ion irradiation, are required to fabricate an electronic circuit. This requirement increases the number and complexity of the processing steps needed and hence the cost of the circuitry. Moreover, this technique cannot be used to selectively vary the conductivity of the polymer to the extent required to produce a microelectronic circuit material capable of functioning at the speeds many current applications require.
While it should be possible to produce polymers with predetermined p or n conductivity patterns by implanting appropriate ions at locations on the polymer where the particular type of conductivity is desired, this method would be extremely expensive and time consuming. The ion doses required to achieve these results would be impractical with the currently available accelerators. Further, the high ion dose rates necessary to produce this selective conductivity could result in destruction of the polymer unless special provisions were made for cooling the polymer, which would add additional processing steps.
Accordingly, there is presently a great need for a method that employs relatively simple processing steps to produce, at low cost, a highly conductive, stable polymer having both n and p conducting regions that is sufficiently light in weight and radiation hardened to be useful in space applications.